The present invention is concerned with a method for the preparation of organic-solvent soluble, highly heat-resistant layered structures by applying radiation-sensitive, soluble preliminary polymers to a substrate in the form of a layer or a foil; irradiating the radiation-sensitive layer or foil through negative patterns; removing the unirradiated layer or foil parts and annealing the relief structures thus obtained.
The preparation of thermally stable polymide structures from soluble, bichromate-sensitized preliminary polymers is known in the art (cf. Polymer Engineering and Science, vol. 11, pages 426 to 430 (1971)). Their use as negative photoresists is made much more difficult by the fact that the solutions and films of these photosensitized preliminary polymers are very unstable and accordingly must be processed immediately after preparation. In addition, the final removal of the resist from the substrate without damaging the latter is difficult, since the polyimides obtained after exposure, developing and annealing usually only dissolve in strong acid or alkaline media, but not in organic solvents.
It is further known that relief structures can be produced from soluble, light-insensitive preliminary stages of polyimides by means of a photoresist technique and then converting them into polyimides by annealing, (see German Auslegeschrift 1,764,977). The limitations as to storage stability of the preliminary polymers and to the ability to remove the polyimides apply here equally, and in addition, only limited resolution and moderate edge definition can be obtained in dissolving the film portions not covered by the photoresist.